Design And Implementation Of EMI Filter For Switch Mode Power Supply

With the rapid development and wide application of switching power supplies, electromagnetic pollution focused by many researchers. How to deal with electromagnetic compatibility problems becomes a passionate research. As the auxiliary circuit switching power supply, EMI power line filter can effectively inhibit transmitting electromagnetic interference of switching power supply. Therefore the research of this paper is of great significance.In this paper, the generation of electromagnetic interference by internal and external factors of switching power supply was analyzed, and the basic design principles of EMI filter circuit structure and related technical were also proposed. On this basis, the status of differential mode and common mode interference separation methods and the shortcoming of these methodswere were discussed. Based on the parallel transmission line theory and the transmission line transformer, we had designed interference separation circuit. The leakage inductance and stray capacitance of winding determines the characteristic impedance of the transmission line, transmission line transformer can overcoming the influence of the traditional transformer’s parasitics. Then use PSpice software to simulate the effect of separation circuit. On this basis, designed and producted the transmission line transformer with the characteristic impedance is 100 ohm. And then producted the separate network.Secondly, According to study Differential-mode power lines enhanced EMI filter, the high frequency model of the switching power supply’s passive components was analyzed. The non-ideal characteristics of passive components will lead the filter performance of EMI filter worse at high frequency. So it has practical significance to study high-frequency characteristics of EMI filter. Because of the three-terminal capacitor excellent high-frequency performance, use three-terminal capacitor to design the EMI filter. Then use PSpice simulation software to simulate Insertion Loss, analyze the effects of yC and equivalent series inductance( ESL). Meanwhile, the methods to eliminate the high-frequency parasitic characteristics were also discussed. Apply circuit network theory respectively to eliminate capacitance, inductance common mode and differential mode inductance parasitics. And used PSpice simulation verifies the correctness of the proposed method.Finally, A EMI filter for 4kW electric car charger system had been designed. Then extract the parasitics of related components, use the optimization methods in this article to optimize the performance of its high frequency, so that the charging system of conduction of electromagnetic interference controlled within the limits permitted by the state, from the measured data, the optimized filter let the charger system complies with the relevant EMC requirements. Actually verify the optimization methods’ correctness.